Pattern identification (PI), also called Bian Zheng ([symbols; see text]), syndrome differentiation, pattern diagnosis, or pattern classification, is the basic principle and the key concept of Chinese medicine (CM). The core of PI is CM syndrome, on which CM theory, therapeutic method, prescribing formula and the use of Chinese herbal medicine are basically based. PI, in fact, is another classification method anticipated to improve the clinical efficacy. How to make an exact PI seems to be very important for taking full advantage of PI in clinical practice. Therefore, the establishment of diagnostic criterion of pattern has been the prerequisite for the standardization of PI. In recent years, a lot of diagnostic criteria of different CM patterns have been formulated. Taking the diagnostic criteria for blood-stasis syndrome as a model, the methodologies and considerations in establishing a pattern diagnostic criterion were discussed in this paper, which might be of great reference value in future PI standardization research.